On March 17, 2026 Greenwich LifeSciences, Inc. (Nasdaq: GLSI) (the "Company"), a clinical-stage biopharmaceutical company focused on its Phase III clinical trial, FLAMINGO-01, which is evaluating GLSI-100, an immunotherapy to prevent breast cancer recurrences, reported a preliminary update showing a continued reduction in the recurrence rate in the fully enrolled, 250 patient, open label non-HLA-A*02 arm of FLAMINGO-01.
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6 Months of Additional Patient Data Since Last Update Shows Recurrence Rate of <1% per Year in Non-HLA-A*02 Patients Treated with GLSI-100, Following Completion of Primary Immunization Series (PIS)
This <1% Annual Recurrence Rate Observed in Non-HLA-A*02 Patients is Statistically Significantly Smaller Than a 4% Annual Recurrence Rate Over a Similar Time Period Observed in the Katherine Study (Kadcyla Treated Arm) Yielding an Approximately 70-80% Reduction in Recurrence Rate as Explained Below
The non-HLA-A*02 arm does not have a direct placebo comparator arm, thus a Kaplan Meier survival analysis is not possible, and the following method was used:
The <1% recurrence rate per year of these 250 treated patients after completing the PIS was compared to the expected historical recurrence rate per year reported for a similar population in the Katherine study who received TDM1 (Kadcyla), which is about 4% recurrences per year or higher in the initial years of the Katherine study. The majority of the treated patients in FLAMINGO-01 also received TDM1 followed by GLSI-100.
As of this data cut, the current recurrence rate of the non-HLA-A*02 patients treated with GLSI-100, following completion of the PIS over an average of 1.2 years of patient exposure, is statistically significantly smaller than a 4% annual recurrence rate over a similar time period observed in the Katherine study (0.7% versus 4% annual recurrence rate over 1.2 patient-years, 83% reduction in recurrence rate, Chi Square, p < 0.005). This preliminary data will continue to be updated and cleaned, so future and final results may vary. Future updates may be presented at upcoming conferences.
This observation is trending similarly to the Phase IIb trial results and hazard ratio where HLA-A*02 patients were treated and where breast cancer recurrences were reduced up to 80% compared to a 20-50% reduction in recurrence rate by other approved products.
Additional information about the non-HLA-A*02 arm follows:
Virtually all of the non-HLA-A*02 patients have completed the primary immunization series, which is the first 6 monthly vaccinations in the study.
Every 6 months approximately 110 patient-years are added to the non-HLA-A*02 patient data base.
Enhertu (T-DXd) treated patients can be enrolled in FLAMINGO-01. In the future, if Enhertu is approved for high risk patients in the adjuvant setting, more Enhertu treated patients could be enrolled in FLAMINGO-01 and may recur at a lower rate than if treated with Kadcyla. The recurrence rate assumptions in the design of FLAMINGO-01 include this possibility as well as other potential improvements in standard of care.
Analysis of the open label data from FLAMINGO-01 has been conducted in a manner that maintains the study blind. The open label recurrence rate, immune response, and safety data is based on the patients enrolled to date in FLAMINGO-01 and the data provided by the clinical sites so far, which is not completed or fully reviewed, and is thus preliminary. While comparing any preliminary FLAMINGO-01 data to the Phase IIb clinical trial data may be possible, these preliminary results are not a prediction of future results, and the results at the end of the study may differ.
About FLAMINGO-01 Open Label Phase III Data
More than 1,000 patients have been screened with a current screen rate of approximately 800 patients per year. The 250 patient non-HLA-A*02 arm is now fully enrolled, where all patients received GLSI-100, which is 5 times more treated patients and recurrence rate data than the approximately 50 patients treated in the Phase IIb trial. The Primary Immunization Series (PIS), which includes the first 6 GLSI-100 injections over the first 6 months and is required to reach peak protection, is followed by 5 booster injections given every 6 months to prolong the immune response, thereby providing longer-term protection.
In the non-HLA-A*02 arm, a preliminary analysis of recurrence rates after the PIS is completed compared to the recurrence rates comparable to those observed in the Katherine study of Kadcyla shows an approximately 70-80% reduction in recurrence rate.
This non-HLA-A*02 arm observation is trending similarly to the Phase IIb trial results and hazard ratio where HLA-A*02 patients were treated and where breast cancer recurrences were reduced up to 80% compared to a 20-50% reduction in recurrence rate by other approved products.
The immune response at baseline prior to any GLSI-100 treatment, the increasing immune response during the PIS, and the safety profile of non-HLA-A*02 patients is trending similarly to the HLA-A*02 arms of FLAMINGO-01 and to the Phase IIb study.
Analysis of the open label data from FLAMINGO-01 has been conducted in a manner that maintains the study blind. The open label recurrence rate, immune response, and safety data is based on the patients enrolled to date in FLAMINGO-01 and the data provided by the clinical sites so far, which is not completed or fully reviewed, and is thus preliminary. While comparing any preliminary FLAMINGO-01 data to the Phase IIb clinical trial data may be possible, these preliminary results are not a prediction of future results, and the results at the end of the study may differ.
About GLSI-100 Phase IIb Study
In the prospective, randomized, single-blinded, placebo-controlled, multi-center (16 sites led by MD Anderson Cancer Center) Phase IIb clinical trial of HLA-A*02 breast cancer patients, 46 HER2/neu 3+ over-expressor patients were treated with GLSI-100, and 50 placebo patients were treated with GM-CSF alone. After 5 years of follow-up, there was an 80% or greater reduction in cancer recurrences in the HER2/neu 3+ patients who were treated with GLSI-100, followed, and remained disease free over the first 6 months, which we believe is the time required to reach peak immunity and thus maximum efficacy and protection. The Phase IIb results can be summarized as follows:
80% or greater reduction in metastatic breast cancer recurrence rate over 5 years of follow-up with a peak immune response at 6 months and well-tolerated safety profile.
The PIS elicited a potent immune response as measured by local skin tests and immunological assays.
About FLAMINGO-01 and GLSI-100
FLAMINGO-01 (NCT05232916) is a Phase III clinical trial designed to evaluate the safety and efficacy of Fast Track designated GLSI-100 (GP2 + GM-CSF) in HER2 positive breast cancer patients who had residual disease or high-risk pathologic complete response at surgery and who have completed both neoadjuvant and postoperative adjuvant trastuzumab based treatment. The trial is led by Baylor College of Medicine and currently includes US and European clinical sites from university-based hospitals and academic and cooperative networks with plans to open up to 150 sites globally. In the double-blinded arms of the Phase III trial, approximately 500 HLA-A*02 patients are planned to be randomized to GLSI-100 or placebo, and up to 250 patients of other HLA types are planned to be treated with GLSI-100 in a third arm. The trial has been designed to detect a hazard ratio of 0.3 in invasive breast cancer-free survival, where 28 events will be required. An interim analysis for superiority and futility will be conducted when at least half of those events, 14, have occurred. This sample size provides 80% power if the annual rate of events in placebo-treated subjects is 2.4% or greater.
For more information on FLAMINGO-01, please visit the Company’s website here and clinicaltrials.gov here. Contact information and an interactive map of the majority of participating clinical sites can be viewed under the "Contacts and Locations" section. Please note that the interactive map is not viewable on mobile screens. Related questions and participation interest can be emailed to: [email protected]
About Breast Cancer and HER2/neu Positivity
One in eight U.S. women will develop invasive breast cancer over her lifetime, with approximately 300,000 new breast cancer patients and 4 million breast cancer survivors. HER2 (human epidermal growth factor receptor 2) protein is a cell surface receptor protein that is expressed in a variety of common cancers, including in 75% of breast cancers at low (1+), intermediate (2+), and high (3+ or over-expressor) levels.
(Press release, Greenwich LifeSciences, MAR 17, 2026, View Source [SID1234663613])